This invention relates to an uninterruptible AC power supply and more particularly to such a power supply wherein a battery-powered high-frequency inverter is used to supplement a failing power provided by an AC utility to maintain a regulated AC power output to the load.
It is known in the prior art to have an uninterruptible AC power supply which provides for a transfer from an AC utility power to a battery-powered high-frequency inverter when the utility power fails. Thus in such prior art power supplies, whether the AC utility power fails completely or partially a complete or substantial transfer is made from the utility power to the inverter. Such an uninterruptible power supply is not only inefficient but places a large demand on the battery so as to shorten the time that it is able to perform. It is highly desirable, therefore, to be able to provide an AC uninterruptible power supply wherein when the utility power partially fails only enough power is drawn from the battery-powered high-frequency inverter to make up for the drop in the utility power.